Method and apparatus for controlling the drying rate in a wet pellet dryer



9, 1969 D. l.. Du'TcHE-R 3,482,327 METHOD AND APPARATUS FOR CONTROLLINGTHE DRYING RATE IN A WET PELLET DRYER Filed March 22,` 1968 4Sheets-Sheet l A 7' TORNEVS R m n m U W m2 m D @n mm v L. N l... mm(5.30.5200 1 D mm o .m S @n n Nm ill Y, vm m B H v w mu zm2 da www NN mm.n m wm mbwllll oEA..I nim mm. ov QL a mx im u .m 10m UOM NvK. 55E @MN wmAl w .Bonomi l mm w v m nmjm t mmQ 5.3mm .A mmrwa w 5521.1. L m v w m Qsv vm. mm N. x93@ mm.\. v m.\. n .m WM. l l I I I I III! Il!! /Em zomm u.T s L, s Nm mv Dec. 9, 1969 D. L. 'DUTCHER 3,482,327

METHOD AND APPARATUS FOR CONTROLLING THE DRYING RATE IN A WET PELLETDRYER Flled March 22. 1968 4 Sheets-Sheet 3 LB/MIN SCF/MIN IOO WIJ

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|000 207 .F x u A A Deu.` 9, 1969 D, L. DUTCHER Y 3,482,327

METHOD AND APPARATUS FOR CONTROLLING THE DRYING RATE IN A WET PELLETDRYER Filed Mann 22, 1968 4 sheets-sheet 4 loo 30| 3H 3:2 LB/MmA\........

2000 302 F l v zooo 303 SCF/MIN l L f-- INVENTOR.

D. L DUTCHER @www United States Patent() METHOD AND APPARATUS FORCONTROLLING THE DRYING RATE IN A WET PELLET DRYER Dennis L. Dutcher, St.Louis, Mo., assignor to Phillips Petroleum Company, a corporation ofDelaware Filed Mar. 22, 1968, Ser. No. 715,360 Int. Cl. F26b 21/10, 7/00U.S. Cl. 34-12 10 Claims ABSTRACT OF THE DISCLOSURE Carbon lblack andwater are admixed in a pelletizer and passed to a pellet dryer. The owrate of water to the pelletizer is measured and a signal is establishedresponsive thereto representative of the temperature of the shell of thedriver in the constant pellet temperature section required to achievethe desired drying rate. The actual shell temperature in the constantpellet temperature section is measured and compared with the predictedsignal. A signal representative of the comparison is utilized to adjustthe supply of heat to the dryer. The heat supply to the outlet end ofthe dryer can be separately controlled responsive to the temperature ofthe product leaving the dryer. Water can be injected into the inlet ofthe dryer in response to a sharp drop in water ow rate to the pelletzer.

This invention relates to method and apparatus for the controlled dryingof agglomerates. In one aspect the invention relates to controlling theheat transfer rate in a carbon black pellet dryer responsive to the rateof addition of water to the pelletzer.

Carbon black as initially produced is a very fine, fluffy powder ofexceedingly low density which readily flies into the atmosphere andpresents numerous diiiculties in handling, shipping and storage, withwhich the industry is familiar. In order to increase its density, reduceflying and minimize handling difficulties, it is conventional to formsmall pellets of the carbon black which are relatively dustless,free-flowing, spheroidal pellets.

Such beads or pellets are usually produced by tumbling or otherwiseagitating the carbon Iblack with a binding agent in a slowly rotatingdrum. The wet pellets from the rotating pelleting drum are then passedto a dryer wherein they are dried and the moisture content is reduced toless than 1 percent and usually about 0.1 percent. Conventional dryerssuch as heated rotating drums are used to remove the moisture from thewell pellets. It is well known to those skilled in the art that thetemperature of the dryer controls the ultimate quality of the driedpellets. If the temperature of the dryer is too hot, the dried pelletsmay be porous and have a spongy texture which offers little resistanceto crumbling. ln extreme cases the drying drum may become so hot as toignite the carbon black. On the other hand, if the dryer is too cold,the resulting pellets may be soft, crumble easily, and cake when stored.The temperature of the pellets as they are discharged from the dryershould be in the range of about 350 to 450 F. with a range of about 375to 425 F. being preferred. Thus, any method to more effectively controlthe temperature of the dryer is a valuable contribution to the art.

One system which has been suggested manipulates the fuel flow rate tothe burner in the dryer responsive to the temperature of the productleaving the dryer or in 3,482,327 Patented Dec. 9, 1969 ice the lastportion of the dryer. However, the extensive dead time involved betweena change in feed to the dryer and the appearance of this change at theeffluent end of the dryer makes such a control system very diicult tomaintain on an effective basis. Systems utilizing purge gas effluenttemperature encounter dii-liculties since the amount of lire box gas andtherefore the purge gas temperature varies with the amount of watervaporized, independent of dryer feed rate. Other systems involving theprediction of fuel rate required responsive to changes in water flowrate to the pelletizer, while generally satisfactory, are faced with theproblems of thermal efficiency varying with load changes and a quadraticrelationship between load and fuel required.

It has now been discovered that an effective control of the dryer can bemaintained by predicting, responsive to the water llow rate to thepelletizer, the dryer shell temperature required t0 achieve a desiredheat transfer rate to the pellets in the initial portion of the dryer.The predicted value is compared against the actual shell temperature toobtain a control signal to manipulate the heat input to the dryer. Thiscan be accomplished by regulating the fuel flow rate to the burner in adirect lired dryer or the fuel flow rate to the furnace in a ue gasheated dryer. The heat input to the effluent end portion of the dryercan be controlled responsive to the temperature of the product leavingthe dryer to serve as a trim control. Water can be injected into thedryer inlet if there is insufficient water in the pellet feed to preventoverheating.

Therefore, it is an object of the invention to provide improved methodand apparatus for controlling the drying of agglomerated material.Another object of the invention is to control the rate of heat transferto pellets in a dryer. Another object of the invention is to preventoverheating of carbon black pellets in a pellet dryer. Other objects,aspects and advantages of the invention will be apparent from a study ofthe specification, the drawing and the appended claims to the invention.

In the drawings FIGURE 1 is a schematic representation of a pelletingsystem in accordance with a presently preferred embodiment of theinvention; FIGURE 2 is a schematic representation of a pelleting systemin accordance with another embodiment of the invention; FIG- URE 3 is agraphical representation of the response of the system of FIGURE 1 to anincrease and a subsequent decrease in carbon black feed rate to thedryer; and FIGURE 4 is a graphical representation of the response of apelletizing system wherein the fuel ow rate is varied responsive to thetemperature of the product leaving the drver.

Referring now to FIGURE 1, loose flocculent carbon black is fed intopellet mill, or mixer, 11 through conduit 12. A liquid binder, forexample water, which can contain a very small amount of molasses, ispassed by way of conduit 13 into mixer 11. The rate of flow of waterthrough conduit 13 is manipulated by means, not shown, responsive to therate of addition of carbon black to the mixer to maintain the ratio ofbinder to carbon black substantially constant at a desired value. Onesuitable system is to vary the ow rate of water responsive to theelectrical power input required to operate the agitator of the mixer.Another system varies the flow rate of water to the pelletizerresponsive to the output of a weigh conveyor in the carbon blacktransporting line. The resulting agglomerates or pellets are passedthrough a line 14 into a polisher 15 wherein the agglomeration action iscontinued. The wet pellets are passed from polsher 15 through line 16into the inlet end of pellet dryer 17.

A suitable fuel, for example natural gas, fuel oil, or the off-gas fromthe carbon black lters, is passed by way of conduit 21 into a furnace22. Air is passed by way of conduit 23 into and through preheater 24 inindirect heat exchange with the hot gases in furnace 22 and then throughconduit 25 into furnace 22 wherein the air is admixed with the fuel toform hot combustion gases. The hot combustion gases contact preheater 24and then pass through line 26 to and through branch conduits 27a through27h into the jacket 28 surrounding the shell 29 of pellet dryer 17. Eachof branch conduits 27a through 27h can be provided with a damper, 30athrough 30h, respectively. The hot combustion gases pass around shell 29and exit jacket 28 by way of conduits 31a, 31b and 31e which .areconnected through conduit 32 to a vent or other point of utilization. Aconduit 33 is connected between conduit 32 and the etlluent end of shell29 to fpass a portion of the hot combustion gases through the interiorof shell 29 in countercurrent ow relationship to the carbon blackpellets. This portion of the combustion gas serves as a purge gas tocarry steam out of the dryer by way of conduit 34. A blower 35 isprovided in conduit 34 to withdraw the purge gas containing steam and tomaintain the pressure in shell 29 slightly below atmospheric pressure toprevent leakage of carbon black from the system. The wet pellets passingthrough conduit 16 to dryer 17 are preferably preheated to a suitabletemperature, for example on the order of 150 F. The preheated wetpellets enter dryer 17, which is rotated on its horizontal axis by meansnot shown. The pellets are rapidly heated upon entry into dryer 17 tothe operating temperature, for example on the order of 200 F. Thepellets achieve the operating temperature within approximately one footof the inlet to the dryer and remain at the operating temperature forapproximately two-thirds of the length of the dryer due to the plateauin the heat input versus temperature relationship resulting from thevaporization of the water. At a point approximately two-thirds of theway through the dryer, suicient moisture has been evaporated to permitan increase in the temperature of the pellets. The pellets are heatedthrough the remainder of the dryer to further lower the water contentand to achieve an euent temperature of the pellets leaving the dryer byway of conduit 36 in the range of about 375 F. to about 425 F.

A llow measuring sensor 41 is operatively connected to conduit 13 andproduces a signal representative of the ow rate of water therethrough.For sake of simplicity, the ow sensor is illustrated as an orifice, itbeing recognized that suitable square rooting mechanism to achieve alinear flow signal can be included in the case of the orifice type flowsensor, or that other flow sensors such as turbine flow sensors can beutilized. Where the water flow rate contains high frequency oscillation,as in the oase where the water ow rate is regulated responsive to theelectrical power input to mixer 11, the ow signal can be passed to afilter 42 to smooth out the ow signal. An example of a suitable filter42 is the Taylor Instrument Company Model 588104 pneumatic pulsationdamping unit. The filtered llow signal is applied to one input of ratiorelay 43. As it is desirable to maintain a minimum temperature of theshell 29 of dryer 17 during start-up or temporary interruptions of thepelletizing operation, ratio relay 43 can be utilized to produce anoutput signal represented by the following relationship:

where SR is the output of ratio relay 43, SF is the linear flow signalfrom ow sensor 41, K1 is a proportionality constant, and K2 is a valueequal to the minimum temperature of shell 29 at zero water llow to mixer11. The minimum temperature for the shell 29 is generally the `4operating temperature, that is, the constant temperature plateau for thewet pellets at which vaporization of the water occurs withoutsignificant heating of the pellets. The output signal SR isrepresentative of the predicted temperature of that portion of shell 29which is coextensive with the constant operating temperature region ofthe wet pellets which will be required to achieve the heat transfer ratenecessary to vaporize the water at the rate it is flowing throughconduit 13. This relationship follows from the equation:

wherein:

.q is time rate of heat transfer, B.t.u./hr.,

As the operating temperature lplateau TP and the other factors remainconstant, it is readily seen `that the heat transfer rate variesdirectly with variations in the temperature of the external surface ofshell 29 in the pellet temperature plateau region of the dryer. Anexample of a suitable ratio relay 43 is the Taylor Instrument CompanyModel NF1151 pneumatic ratio unit.

The output signal of ratio relay 43 is applied to the set point input oftemperature recorder controller 46. A temperature sensor 47, for examplea Honeywell Model RL-l radiation pyrometer, senses the external skintemperature of shell 29 at a position which is within the constantpellet temperature plateau region of the dryer. The electrical output oftemperature sensor 47 is applied to the signal input ofmillivolt-topressure transducer 48. A bias value is applied to biasinput 49 of transducer 48 and the output of transducer 48 is applied tothe input of square root extractor 51 with the output of square rootextractor 51 being applied to the measurement input of temperaturerecorder controller 46. While, in accordance with the Stefan-Boltzmannlaw, the detected energy is representative of the fourth power of thetemperature, it has been found, for the operating range encountered inthe carbon black pellet dryer, the square root of the difference betweenthe output of the radiation pyrometer and the bias value 49 issufliciently linear for the desired control purpose. However, ifdesired, two square root extractors could be utilized in series toobtain the fourth root of the output of the pyrometer. An example of asuitable transducer 48 is the Taylor Instrument Company Model 700TD1333millivolt-to-pressure transducer. Square root extractor 51 can be aTaylor Instrument Company Model 359RF pneumatic square root extractor.The output of temperature controller 46 is representative of acomparison of the actual shell temperature represented by the output ofsquare root extractor 51 and the predicted shell temperature representedby the output of relay 43. Controller 46 can be a two mode controllerwith proportional plus reset. The output of temperature controller 46 isapplied to the setpoint input of flow recorder controller 52 whichmanipulates valve 53, operatively located in conduit 21, responsive to acomparison of the actual flow rate of the fuel in conduit 21, asindicated by tlow sensor 54, with the setpoint signal. The output offlow sensor 54 is applied to the measurement input of ratio controller55. A signal representative of the desired ratio of air to fuel isapplied to setpoint input 56 of controller 55. The output of controller55 represents the required air flow rate and is applied to the setpointinput of the ow recorder controller 57, which manipulates the valve 58,located in conduit 23, responsive to a comparison of the setpoint signalwith the actual flow rate as indicated by ow sensor 59. An example of asuitable controller 55 is a Taylor Instrument Company Model 105NF1151pneumatic ratio unit. Where significant delay is encountered between ameasurement by flow sensor 41 and the corresponding water reaching dryer17, suitable first order or multiple order lags can be inserted in thecontrol system to account for such delay.

Referring now to FIGURE 2, there is illustrated a modified version ofthe system of FIGURE 1. Flocculent carbon black is passed throughconduits 112a and 112b to mixers 111a and 111b, respectively. Water ispassed through conduits 113a and 113b to mixers 111a and 111b. Theoutput of mixers 111a and 111b is passed to polisher 115 with the outputof the latter being passed through line 116 to pellet dryer 117. Asuitable fuel is passed through conduits 120 and 121 into and throughbranch conduits 127a through 127f to burners 161a through 161f,respectively, located inside of the lower portion of jacket 128 whichsurrounds shell 129. Air is admitted into jacket 128 by way of opening123. The combustion gases are withdrawn from jacket 128 by way ofconduits 131a through 131d and passed into conduit 132. A portion of thehot combustion gases are withdrawn from conduit 132 and passed by Way ofconduit 133 into the effluent end of shell 129 for countercurrent flowto the carbon black pellets in shell 129 as purge gas. Conduit 134connects the inlet end of shell 129 to blower 135 for the Withdrawal ofthe purge gas and steam from the shell 129.

A rst signal representative of the flow rate of Water through conduit113a is transmitted by flow sensor 141a to adder 162. A second signalrepresentative of the How rate of water through conduit 113b istransmitted by flow sensor 141b to a second input of adder 162. As inthe case of the system of FIGURE 1, filtering means can `be utilized tosmooth out the water flow rate signals if desired. The output of adder162 represents the total water flow rate to the mixers and is applied toone input of adder 163, through delay 164 to a rst input of subtractor165, and directly to a second input of Subtractor 165. The output ofSubtractor 165 represents the difference between the instantaneous waterflow rate and a delayed function of a previously existing water ow rate,and thus is indicative of any significant changes in the water flow rateto the mixers. Subtractor 165 is biased to produce an output signal onlywhen the instantaneous ow rate signal is less than the delayed flow ratesignal or, in other words, when a decrease in the total Water flow rateto the mixers has occurred. The output signal of subtractor 165 returnsto zero -When the delayed flow rate signal drops to the value of theinstantaneous flow rate signal. The output of Subtractor 165 is appliedto the set point input of flow recorder controller 166 which manipulatesvalve 167 positioned in conduit 168 responsive to a comparison of theset point and the actual flow rate through conduit 168 as indicated byflow sensor 169. Thus, upon the occurrence of a positive output ofSubtractor 165, flow controller 166 opens valve 167 to` pass waterthrough conduit 168 into the inlet end of shell 129. This preventsoverheating of the carbon black pellets during the time require-d forthe Iburner heating system to respond to the control system. The outputof Subtractor 165 is also applied to a second input of adder 163 toproduce a signal representative of the total ow rate of water beingintroduced into dryer 129 by way of conduits 113a, 113b and 168. Theoutput of adder 163 is applied to an input of ratio relay 143 to producean output signal representative of the temperature of the outer surfaceof a portion of the section of the shell 129 which is coextensive withthe constant pellet temperature plateau operating region which isrequired to vaporize the water from the pellets at the rate it is beingintroduced by way of conduits 113a, 11311 and 168. Ratio relay 143 hasthe same relationship between its signal input and output as ratio relay43. A tem-perature sensor 147 senses the radiation from the externalsurface of shell 129 and transmits a signal representative thereof totransducer 148. Bias value is applied to bias input 149 and the outputof transducer 148 is applied to the input of square root extractor 151.The output of square root extractor 151 is representative of thetemperature of the external surface of shell 129 in the constant pellettemperature plateau region and is applied to the measurement input oftemperature controller 146. The output of temperature controller 146manipulates valve 171 located in conduit 121 to thereby vary the rate offlow of fuel to burners 127a through 1271 to maintain the actual shelltemperature at the predicted value.

Conduit 172 supplies fuel from conduit 120 to burners 161g and 161klocated in jacket 128 under the eluent end of shell 129. Valve 173,located in conduit 172, can be manipulated by temperature recordercontroller 174 responsive to a comparison of the desired producttemperature represented by set point 175 and the actual temperature ofthe dried pellets passing through conduit 136 as indicated bytemperature sensor 176. Thus, valve 171 manipulates the rate of flow offuel to burners 161:1 through 1611 to thereby vary the shell temperaturein the constant pellet temperature plateau region while valve 173 variesthe rate of flow of fuel to burners 161g and 161k to vary the shelltemperature in the effluent end of the shell downstream of the constantpellet temperature plateau region. In this manner, control of valve 171regulates the rate of transfer of heat to the wet pellets while water isbeing evaporated at a substantially constant temperature, and valve 173regulates the transfer of heat to the pellets which have passed out ofthe constant pellet temperature plateau region to control the finaltemperature of the pellets as they leave the dryer.

Referring now to FIGURE 3, curve 201 lis a graphical representation ofthe flocculent carbon black feed rate through conduit 12 to mixer 11 inthe system illustrated in FIGURE 1. Curve 202 represents the temperatureof the hot combustion gases passing through conduit 26 while curve 203represents the ow rate of the hot combustion gases through conduit 26.Curve 204 represents the rate of removal of water by way of the steamand purge gas mixture passing through conduit 34. Curve `205 representsthe temperature of the gases passing through conduit 34. Curve 206represents the location in the last twenty feet of the dryer, which issixty feet long, at which the temperature of the pellets begins to riseabove the constant operating temperature plateau. lCurve 207 representsthe temperature of the pellets as they leave the dryer and enter conduit36. Curve 201 contains a step increase 211 in the carbon black feed rateand a step decrease 212 in the carbon black feed rate. Curves 202through 207 show the response of the respective factors of the system tothese step changes under the control system illustrated in FIGURE l.

Referring now to FIGURE 4 there are illustrated graphicalrepresentations of the various factors in the drying system of FIGURE 1utilized to obtain the curves of FIGURE 3 except that the controlelements 41, 42, 43, 46, 47, 48 and 51 were omitted and the set point offlow controller 52 was adjusted by the output of a temperaturecontroller responsive to the temperature of the pellets passing throughconduit 36. Curve 301 represents the occulent carbon black feed rate andcontains a step increase 311 and a step decrease 312. Curve 302represents the temperature of the combustion gases passing throughconduit 26 while curve 303 represents the llow rate of these combustiongases. Curve 304 represents the rate of removal of water through conduit34 while curve 305 represents the temperature of the gases passingthrough conduit 34. Curve 306 represents the position in the lastportion of the reactor at which the carbon black becomes substantiallydry and the temperature thereof begins to increase. Curve 307 representsthe temperature of the pellets passing through conduit 36.

An examination of the effects on the various factors due to the stepincrease and step decrease in carbon black flow rate for the controlsystem represented by FIG- URE 3 and the control system represented byFIGURE 4 readily indicates the superiority of the control systemrepresented by FIGURE 3 over that of the control system represented byFIGURE 4. This is particularly apparent in..the effect on the producttemperature of the pellets leaving the dryer and the location in thedryer at which the temperature of the pellets begins to increase abovethe constant operating temperature plateau.

Reasonable variations and modifications are possible within the scope ofthe foregoing disclosure and the drawings of the invention.

I claim:

1. I n an apparatus for agglomerating finely divided solids, whichcomprises a mixer; means for introducing said finely divided solids intosaid mixer; conduit means for introducing a liquid binder into saidm'urer; a dryer having an elongated shell; means for passing wetagglomerates from said mixer into the inlet end of said elongated Shell;means for withdrawing dried agglomerates from the outlet end of saidelongated shell; and heating means for heating the exterior surface ofsaid elongated shell; the improved control system comprising means forproducing a first signal representative of the flow rate of said liquidbinder through said conduit means to said mixer; means responsive tosaid first signal to establish i a second signal representative of thetemperature of the external surface of said shell in the region of saidshell wherein the temperature of the wet agglomerates remainssubstantially constant while a portion of the liquid binder contained inthe wet agglomerates is being vaporized, required to vaporize the binderin said region at the rate binder is added to said finely dividedsolids; means for establishing a third signal representative of theactual temperature of the exterior surface of said shell in said region;means responsive to said second and third signals for controlling saidheating means to vary the heat supplied to said shell in said regionresponsive to the difference between said second and third signals.

.2. Apparatus in accordance with claim 1 wherein said mlxer is a pelletmill, said dryer further comprises a jacket surrounding said elongatedshell, said heating means comprises means for passing hot fluid throughsaid jacket in contact with the external surface of said shell, and saidmeans for controlling said heating means comprises means for controllingthe rate of fiow of fuel to said heating means responsive to thedifference between said second and third signals.

3. Apparatus in accordance with claim 1 wherein said means to establisha second signal comprises a ratio relay having an input and an output,means for connecting the output of said means for producing a firstsignal to said lnput of said ratio relay, the output signal from saidratio relay being said second signal and representable as:

SR=K1SFK2 wherein:

SR is said second signal, K1 is a proportionality factor,

` K2 is the desired temperature of said shell at zero flow rate ofbinder through said conduit means, and SF is said first signalrepresentative of the flow rate of binder through said conduit means.

4. Apparatus in accordance with claim 3 wherein said means forestablishing a third signal comprises a radiation pyrometer positionedto detect the radiation from the external surface of said shell in saidregion; a voltage to pressure transducer having a signal input, a biasinput and a pressure output; means connecting the output of saidradiation pyrometer to said signal input of said transducer; means forapplying a bias signal to said bias input of said transducer; a squareextractor with the input thereof connected to said pressure output ofsaid transducer.

5. Apparatus in accordance with claim 4 wherein said means forcontrolling said heating means comprises a temperature controller havinga measurement input, a setpoint and an output; means for applying saidsecond signal to said setpoint; means for connecting the output of saidsquare root extractor to said measurement input; and means responsive tosaid output of said temperature controller to control said heatingmeans.

6. Apparatus in accordance with claim 5 wherein said heating meanscomprises a furnace, second conduit means for passing fuel to saidfurnace, third conduit means for passing air to said furnace, a jacketsurrounding said shell, fourth conduit means lfor passing hot combustiongases from said furnace through said jacket in heat exchangerelationship with the, exterior surface of said shell, and wherein saidmeans to control said heating means comprises means responsive to theoutput of said temperature controller for varyingthe ow rate of fuelthrough said second conduit means, and means responsive to the ow rateof fuel through said second conduit means to vary the rate of flow ofair lthrough said third conduit means to maintain a desired ratio of airto fuel going into said furnace.

7. Apparatus in accordance with claim 1 wherein said mixer comprises `aplurality of pellet mills, said means for introducing finely dividedsolids comprises means for introducing finely divided solids into eachof said plurality of pellet mills, said conduit means comprises aplurality of conduits` each connected to a respective one of said pelletmills, saidmeans for passing Wet agglomerates connects the output ofeach of said pellet mills to the inlet end of said elongated shell, andsaid means for producing a first signal comprises a plurality of flowsensors each being connected to a respective one of said plurality ofconduits, an adder having a plurality of inputs, and means connectingthe output of each of said flow sensors to a respective one of saidplurality of inputs of said adder.

8. Apparatus in accordance with claim 1 wherein said means for producinga` first signal comprises means for sensing the flow rate of liquidbinder through said conduit means and establishing a fourth signalrepresentative thereof, delay means, a subtractor, an adder, means forapplying said fourth signal to the input of said delay means, to aninput of said subtractor and to an input of said adder, means connectingthe output of said delay applying the output of said subtractor to asecond input of means to a second input of said subtractor, means forsaid adder, the output of said adder being said first signal, and meansfor injecting liquid binder into the inlet end of said elongated shellresponsive to the output of said subtractor.

9. Apparatus in accordance with claim 1 wherein said heating meanscomprises first heating means for heating said shell in said region anda second heating means for heating said shell downstream of said region,said means responsive to said second and third signals for controllingsaid heating means comprises means for regulating said first heatingmeans responsive to the difference between said second and thirdsignals, and further comprising means for regulating said second heatingmeans responsive to the temperature of the agglomerates being withdrawnfrom said outlet end of said elongated shell.

10. In a method of pelleting carbon black which comprises passing finelydivided carbon black to a pelletizing zone, passing a liquid binder intosaid pelletizing zone and therein admixing said finely divided carbonblack and said liquid binder to form pellets, passing the thus formedpellets into the inlet end of an elongated drum dryer, passing a heatingfiuid into heat exchanging relationship with the exterior surface ofsaid elongated drum dryer, and withdrawing dried pellets from the outletend of said elongated drum dryer; the improved control procedurecomprising measuring the rate of ow of said liquid binder into saidpelletizing zone and establishing a rst signal representative thereof,establishing responsive to said 'rst signal a second signalrepresentative of the temperature of the external surface of said drumdryer in the region of said drum dryer wherein the temperature of thewet pellets remains substantially constant while a portion of the liquidbinder contained in the wet pellets is being vaporized, required tovaporize the binder in said region at the rate binder is being passed tosaid pelletizing zone, establishing a third signal representative of theactual temperature of the exterior surface of said drum dryer in saidregion, and varying the degree of heating of said References CitedUNITED STATES PATENTS 8/1959 Heller 34-12 3/ 1965 McGregor et al. 263-34JOHN J. CAMBY, Primary Examiner U.S. C1. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 31482327 Dated December 9, 1969 Inventor(s) Dennis L. Butcher It; iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as show-n below:

Column 8 delete line 49; Column 8 after line 50 insert applying theoutput of said subtractor to a second input of -f.

' SIGNED AND SEALED APR 281970 5m) Attest:

Edward M member Ir" WILLIAM E. som, JR. Attestng Officer Commiszeionecr`of Patents

